Scanning Electrochemical Microscopy of Precursor Sites for Pitting Corrosion on Titanium

Scanning electrochemical microscopy, SECM, of oxide-covered titanium foils (~50 A oxide thickness) immersed in potassium bromide solutions is reported. Electrogeneration of bromine (2 Br^-→ Br₂+ 2e^-) at the TiO₂ film is shown to occur rapidly at a few microscopic surface sites. The regions of intense faradaic activity observed in SECM images correlate directly with the location of pit nucleation. The direct correspondence between sites of faradaic activity and oxide breakdown provides a means of identifying precursor sites for pit formation.